1. Field of the Invention
The present invention relates to a silicon integrated circuit for providing a temperature compensated voltage regulator and, more particularly, to an enhanced normalized temperature coefficient voltage regulator.
2. Description of the Prior Art
In many electronic circuits, a high negative temperature coefficient voltage regulator diode is needed. For example, in a high voltage protection circuit, an avalanche diode is often used in the trigger circuit of a silicon controlled rectifier (SCR). The large positive temperature coefficient of avalanche diodes results in the trigger voltage of the protection circuit having a large positive temperature coefficient. In addition to the temperature coefficient problem, there is a large variability in the trigger current of large SCRs which, when coupled with the relatively large series resistance of avalanche diodes, leads to a significant variability of the protection circuit trigger voltage.
A wide variety of temperature compensation circuits exist in the prior art, one exemplary arrangement disclosed in U.S. Pat. No. 4,207,538 issued to J. Goel on June 10, 1980. In the Goel arrangement, a positive temperature coefficient resistance element such as a sensitor and a negative coefficient resistance element such as a thermistor are arranged in a potential divider network, the output terminal of which produces a potential which is a function of temperature. The potential is applied as a bias potential to the control electrode of an amplifier circuit subject to variations in gain as a function of both control electrode voltage and temperature. The potential divider network, therefore, functions to reduce the gain of the amplifier, as a function of temperature.
An alternative arrangement is disclosed in U.S. Pat. No. 4,282,477 issued to A. A. A. Ahmed on Aug. 4, 1981. Here, emitter-coupled differential amplifier transistors have their collector currents differentially combined for application to a series regulator transistor in series with a potential divider network having first and second taps to the base electrodes of the emitter-coupled differential amplifier transistors, for completing a feedback loop which develops positive-temperature-coefficient voltages across resistor portions of the potential divider network. These positive-temperature-coefficient voltages augment negative-temperature-coefficient voltages developed across semiconductor diode means included in the potential divider network to provide for zero-temperature-coefficient voltages being developed across the potential divider network or a portion thereof.
U.S. Pat. No. 4,100,477 issued to R. K. Tam on July 11, 1978 discloses yet another arrangement related to a fully regulated temperature compensated voltage regulator. In the Tam arrangement, the compensation is achieved by the provision of a supply feedback amplifier, coupled to a voltage regulator whose resistances carefully match the resistances of the regulator so that fluctuation in the supply voltage is sensed by the supply feedback section which is dependent only on such matching. This matching provides matching current flow in the regulator and feedback corresponding to variations in current so that current flow through the shunt transistor of the regulator is constant.
There remains in the prior art, the problem of obtaining an enhanced normalized temperature coefficient. A simple temperature coefficient of voltage is normally expressed in units of volts per degree or millivolts per degree while a normalized temperature coefficient is usually expressed as parts per million per degree or percent per degree. An enhanced normalized temperature coefficient is one which is greater than the inherent normalized temperature coefficient of the devices from which it is created. Since no very high temperature coefficient components are available in silicon integrated circuit technology, a special circuit is needed to achieve an enhanced normalized voltage temperature coefficient.